Obesity is the dominant cause of acquired insulin resistance and it is the epidemic of obesity in the United States which is driving the dramatically increasing incidence of Type 2 diabetes. The central theme of this proposal is that chronic low-grade tissue inflammation is an important underlying etiologic factor leading to decreased insulin sensitivity. Our previous work has shown that genetically disabling macrophage inflamma- tory pathways in knockout mice protects animals from obesity and high fat diet induced insulin resistance, lead- ing to the idea that the tissue macrophage can be an orchestrating or initiating cell type underlying this inflam- mation-induced insulin resistance. In this application, we propose a series of novel in vitro and in vivo studies to more fully understand the basic mechanisms of regulation of inflammation. Towards this end, the proposed studies capitalize on our new finding that GPR120, a lipid sensing GPCR expressed in proinflammatory macro- phages, functions as the omega 3 fatty acid receptor. Omega 3 fatty acids are potent anti-inflammatory mole- cules and our studies show that these anti-inflammatory effects are largely mediated through GPR120. Stud- ies are proposed to assess the mechanisms of GPR120 signaling to decipher precisely how signals from this receptor intersect with the inflammatory pathway. We will also conduct extensive in vivo phenotyping studies in GPR120 knockout. In a parallel effort, FOX01 is a well known insulin regulatable transcription factor and PPAR3 is a nuclear receptor mediating anti-inflammatory effects and insulin sensitization. We have made the novel finding that FOX01 can function as a direct transrepressor of PPAR3 activity through protein/protein in- teractions, independent of DNA binding. We propose a number of new studies to explore this finding by using Chip sequencing to define the global promoter binding sites (cistrome) of both FOX01 and PPAR3. We will also conduct in vivo studies using wild type and mutant FOX01 in a doxycycline inducible transgenic system to assess the effects of FOX01 repression of PPAR3 on overall in vivo insulin sensitivity TZD-responsiveness and glucose homeostasis. Finally, CD11c+ macrophage represents the majority of the macrophages recruited into obese adipose tissues. These cells are highly proinflammatory releasing large amounts of tissue cytokines which can cause insulin resistance through paracrine mechanisms. An improved understanding of the biology of these cells should provide new mechanistic insights into the etiology of inflammation/insulin resistance. To- wards this end, we have identified novel secretory and extracellular matrix proteins (biglycan and galectin 3) and a new GPCR (GPR105) which are differentially highly expressed in CD11c positive macrophages and have generated colonies of KO mice for new in vivo and in vitro studies. These results should identify relevant mechanisms where-by modification of inflammatory pathways in macrophages and in insulin target cells regu- lates systemic insulin resistance. This knowledge should lead to a better understanding of insulin resistance in Type 2 diabetes and could potentially lead to novel therapeutic approaches. PUBLIC HEALTH RELEVANCE: Obesity is the dominant cause of acquired insulin resistance and the epidemic of obesity in the United States is driving the dramatic increase in incidence of Type 2 diabetes. Chronic low-grade tissue inflammation is a major cause of insulin resistance and the studies in this application will identify new mechanisms underlying the regulation of inflammation and how inflammation causes insulin resistance. These studies should lead to an improved understanding of the basic causes of Type 2 diabetes mellitus and hold the potential for new therapeutic modalities.